Silver is used extensively for industrial purposes owing to its exceptional properties (e.g., high electrical and thermal conductivity, malleability, ductility, and its resistance to corrosion). To illustrate, common uses for, or products incorporating, silver or silver compounds include photographic materials, electroplating, electrical conductors, dental alloys, solder and brazing alloys, paints, jewelry, coins, mirror production, antibacterial agents, and water purification.
The range of methods used to produce metallic silver include chemical, physical (atomization and milling), electrochemical, and thermal decomposition techniques. Each type of method generally produces particles with a characteristic morphology and purity that ultimately govern its functional properties. Among the various existing techniques, those based on chemical precipitation offer distinct advantages in terms of particle morphology, manufacturing cost, and scale-up efficiency for mass production.
Precipitation of metallic silver in solution generally involves a chemical reduction in which a dissolved silver salt species is treated with a reducing agent to generate metallic silver, which precipitates out from the solution. Though existing methods are relatively simple and incorporate quick reduction reactions, the reducing agents employed for such methods are frequently toxic and/or carcinogenic, and can cause safety and health problems when implemented in high volumes.
To address these concerns, methods that use alcohols or polyols have been developed. These methods generally involve the reduction of a silver salt species using a heated alcohol or polyol, which serves as both the reducing agent and solvent, in the presence of protecting ligands. A major drawback of these alcohol or polyol methods is that large quantities of organic solvents are used to dissolve the metal salts, and thus large quantities of chemical waste are generated.
There accordingly remains a need for improved technologies that can be used to produce metallic silver. It would be particularly advantageous if these methods were more simple, less chemical-intensive, and less expensive, while also being amenable to commercial-scale production of metallic silver. It is to the provision of such technologies that the present disclosure is directed.